The invention relates to a self-clamping wrench having a fixed clamping jaw, which is rigidly connected to a handle, and a mobile clamping jaw, which is pivotally mounted thereon whereby said mobile clamping jaw is pushed into its closed position by a tension spring. A spring-loaded hand lever is pivotally mounted to the handle, which engages the mobile clamping jaw.
Self-clamping wrenches are well known in a great number of various configurations. They have in common that the moment (torque) exerted on the workpiece during actuation of the wrench increases the tensioning force of the mobile clamping jaw. Such self-clamping wrenches are designed, for example, as spanner wrenches or pipe wrenches.
During manipulation of the wrench there is the need that the mouth of the wrench, which is formed between the fixed clamping jaw and the mobile clamping jaw, is kept open against the effects of the tension spring when the wrench is placed on the workpiece or when it is removed. During adjustment of the wrench between subsequent turning movements it is often times also an advantage if the mouth of the wrench can be opened against the effect of the tension spring, for example, to prevent damage to sensitive workpieces in case of toothed clamping jaws as, for instance, in plumbing or in the use on bolts made of synthetic material.
On a known self-clamping wrench of the type mentioned in the beginning and as disclosed in U.S. Pat. No. 4,616,534, there is for this purpose a hand lever mounted on the handle at the opposite side of the mobile clamping jaw, which may be pushed toward the handle against the force of the lever spring. An arm of the lever engages thereby a protrusion on the mobile clamping jaw facing the handle to swing said clamping jaw into an open position and to keep it open. The self-clamping function of the mobile clamping jaw is activated by the effect of the tension spring only when the hand lever is released.
Manipulation of this wrench is relatively complicated since the hand (operating) lever must be moved and held in place against the force of its lever spring to open or keep open the mouth of the wrench. Should the hand lever be released unintentionally during the use of the wrench, for example during re-gripping between two subsequent turning movements, then the mount of the wrench closes shut. This is disturbing during the operation of the wrench and it may cause damage to sensitive workpieces, particularly when toothed clamping jaws are used.
On another known wrench (disclosed in DE-A-1 299 570), which is not self-clamping, a hand lever mounted on the handle is used to close the mouth of the wrench in a movement similar to that of pliers until it grasps the workpiece and then locks the slidable--but not pivotable--mobile clamping jaw with a cam that is joined to the hand lever. The transmission of motion between the hand lever and the mobile clamping jaw is caused by a leaf spring that is attached to the hand lever, which engages a recess on the mobile clamping jaw that faces the handle.
On another known closed-end jaw wrench, disclosed in U.S. Pat. No. 4,594,922, the handle lever mounted on the handle body is used to move a pivotable closed-end jaw into a clamping position. The hand lever has to be held in place by a locking device. A tension spring does not exist to push the closed-end jaw into the clamping position by the force of a spring.
The object of the invention is to design a self-clamping wrench of the type mentioned in the beginning whereby it can be manipulated in a simple manner and whereby the self-clamping effect occurs only when the wrench is placed on the workpiece for the performance of a moment (torque); otherwise, the mouth of the wrench should open automatically and should remain in an open position.